1. Field
The following description relates to an anti-collision system and method which reduce the collision of data transmitted by radio frequency identification (RFID) tags.
2. Discussion of Related Art
Similar to a bar code, a magnetic card, and the like, an RFID system may be used for automatic identification, and may be applied to many fields such as individual identification, product identification, location tracing, and financial services. A field that is currently drawing a lot of attention is physical distribution management, and the like, in which RFID systems are being used to replace existing bar code systems.
An RFID system may simultaneously identify a plurality of RFID tags that are present in a predetermined area. While an existing bar code system requires a line of sight (LOS) between a scanner and an object to be identified, the RFID system may identify an RFID tag without a LOS using a radio wave. Also, it is possible to identify a moving RFID tag in the predetermined area, which allows for a faster identification speed than existing identification systems.
In an RFID system, when an RFID reader attempts to identify an RFID tag in an RF area, and a plurality of RFID tags present in the RF area simultaneously transmit their identification information (identities (IDs)) to the RFID reader, the identification information may collide with each other which may prevent the RFID tags from being properly identified.
To prevent a collision of information, an RFID system may use anti-collision technology. Thus far, research has been conducted on anti-collision technology for a static situation in which an RFID tag does not move. However, an RFID system that continuously traces product movement, for example, on a conveyor belt system, and the like, must identify an RFID tag during a short time in which the RFID tag passes through the area of an RFID reader. In this example, the RFID reader fails in identification unless the RFID tag is identified in the predetermined time.
RFID anti-collision mechanisms are generally classified into framed slotted ALOHA (FSA)-based mechanisms and binary tree-based mechanisms. In a dynamic FSA (DFSA) mechanism, the number of RFID tags must be estimated to select an optimum frame size. However, when RFID tags move dynamically, it is difficult to accurately estimate the number of RFID tags.
Also, in the existing DFSA mechanism, there is no priority between an RFID tag that has undergone many collisions and an RFID tag that has not undergone many collisions. Thus, there is a high probability that an RFID tag in the identification area of an RFID reader that has undergone many collisions will compete with RFID tags that are new to the identification area. Accordingly, an RFID tag may fail to be identified, and may move out of the identification area due to its movement.
In an existing binary tree mechanism, once identification begins, RFID tags that newly flow in the identification area of an RFID reader cannot be identified until all RFID tags present in the identification area at the start of identification are identified. Because it is not possible to adjust the time to attempt identification and the number of times to attempt identification, the existing binary tree mechanism is not appropriate for a situation in which RFID tags dynamically move.